Light source devices that use a phosphor are known as light source devices for projectors. This type of light source device has a phosphor wheel and an excitation light source that irradiates excitation light upon the phosphor wheel.
The phosphor wheel includes a wheel, and a phosphor layer that is formed on the wheel surface and that contains a phosphor that emits fluorescent light in response to excitation light. The phosphor wheel is configured such that the wheel rotates at a fixed speed with the center of the wheel surface as the center of rotation. The phosphor layer may be formed by applying a phosphor directly to the wheel surface, or may be formed by adhering a sheet to which a phosphor has been applied to the wheel surface.
A drive current that is supplied to the excitation light source is controlled such that the intensity of the excitation light is uniform. However, because the thickness of the phosphor layer or the concentration of the phosphor may vary according to the position on the phosphor wheel, the intensity of the fluorescent light will vary according to the position of irradiation of excitation light on the phosphor wheel even when the intensity of the excitation light is uniform. As a result, when excitation light is irradiated upon a phosphor wheel that rotates at a fixed speed, the intensity of the fluorescent light changes cyclically, and this cyclical change in the intensity of the fluorescent light may give rise to a phenomenon known as “flicker” that is perceptible to the human eye as flashing light. This same flicker may occur due to damage to the phosphor layer or to gaps in the joining seams of a sheet.
A light source device that can prevent the above-described flicker is disclosed in Patent Document 1. In this light source device, a light sensor that detects fluorescent light is arranged in the vicinity of a collimator lens that converts the fluorescent light emitted by the phosphor wheel to parallel luminous flux. The light sensor converts the fluorescent light to an electrical signal, and this output signal is proportional to the intensity of the fluorescent light. On the basis of the output signal of this light sensor, the drive current that is supplied to the excitation light source is controlled such that the intensity of the fluorescent light becomes uniform.